Digital printing involves technologies in which a printed image is created directly from digital data, for example using an electronic layout and/or a desktop publishing program. Some known methods of digital printing include full-color ink jet printing, electrophotographic printing, laser printing, and thermal transfer printing methods.
Regarding ink jet printing or ink jet transfer technologies, e.g., ink jet printing on an intermediate transfer medium, it is noted that certain types of inks upon ejection from an ink jet orifice often produce satellite droplets that can degrade print quality. For example, satellite droplets can land downstream or upstream from a primary drop and can be manifest on a print as multiple dots, dot expansion in the print direction (dot ellipticity), or background darkening. Furthermore, satellite droplets less than a micron in diameter (aerosol) can contaminate print engines.
Various attempts to reduce satellite droplets in various types of printing have been explored. Some methods have included reducing the drop velocity of the jetting ink, or decreasing the distance between the print head and substrate. However, these approaches have drawbacks, including magnification of drop placement errors caused by non-uniformities in drop velocity, trajectory, and airflow that are present among the thousands of nozzles that span a print bar, or increasing chances of print head damage due to contact wit print substrate. Alternatively, additives have been used to modify the surface tension and/or viscosity of inks. However, typically large amounts are added to make an appreciable difference, which can have a negative impact on image quality and ink adhesion. Active satellite removal using air jets or electrostatic forces also has challenges including increased cost and complexity, and does not adequately address the problems associated with long drop tails or large satellite drops.